tools: include necessary headers explicitly

Several host-tools use "bool" type without including <stdbool.h>.
This relies on the crappy header inclusion chain.

tools/Makefile has the following line:

  HOST_EXTRACFLAGS += -include $(srctree)/include/libfdt_env.h \

All host-tools are forced to include libfdt_env.h even if they are
totally unrelated to FDT.  Then, <stdbool.h> is indirectly included
as follows:

     include/libfdt_env.h
  -> include/linux/types.h
  -> <stdbool.h>

I am fixing this horrible crap.  In advance, I need to add necessary
include directives explicitly.  tools/fdtgrep.c needs more; <fctl.h>
for open() and <errno.h> for errno.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>